I realize this question is from a while ago, but I thought I would answer it as maybe the person is still looking for an answer.
The difference between DDR I, II and III
DDR I is the oldest of the RAM sticks and has 184 pins, has the slowest chip timing and requires more voltage from the motherboard.
DDR II Is newer and has a faster chip speed, lower voltage required by the motherboard and has 240 pins
DDR III is the newest RAM It has the fastest chip speeds, lowest voltage requirement and also has 240 pins
There are a few ways to tell the difference between the three versions of the RAM
There is usually a sticker on the RAM stick with a part number of some sort. You can Google the part number and it will tell you what you have. Another way to tell is the slot in the row of pins. If it is DDR II the slot will be closer to the right side in the row of pins.. If it is DDR III the slot will be closer to the left side. This gets confusing because sometimes you can't tell which is the front side of the RAM from the back side. To tell the difference, you look for a small number between the edge of the RAM stick and the row of pins. You are looking for a number 1. When find that, then you will have the front side of the RAM.
If you are trying to tell what type of RAM you have in your pc, reboot it and watch for the BIOS information to come up before it boots to windows. It will tell you what type of RAM you have and the speed. If you need to pause the boot process so you can read it, you can press Pause / break and that should pause the process so you can read the screen or write the info down..
I hope this information was helpful to you. If you have any questions, please don't hesitate to ask..